Pink-pigmented facultative methylotrophs (PPFMs) of the type Methylobacterium mesophilicum are bacteria normally found on plant surfaces. It has been demonstrated that these bacteria interact with plants, by 1) producing a variety of compounds that affect plant metabolism; and by 2) consuming plant metabolic waste, most notably methanol. Production compounds include, but are not limited to vitamins (Basile et al 1985. Bryologist 88(2):77-81.), enzymes (Holland and Polacco 1992. Plant Physiol. 98:942-948.), and cytokinins (Long et al 1996. In: Lidstrom and Tabita eds. Microbial Growth on C1 Compounds, Kluwer Academic Publishers). Strains of the bacteria have also been identified that produce amino acids (Izumi, 1985 J. Ferment. Technol. 63:507-513, U.S. Pat. No. 3,663,370; U.S. Pat. No. 3,907,673; U.S. Pat. No. 3,907,641 all of which are incorporated herein by reference).
The inventors have previously described a method for altering the metabolism of a plant (U.S. Pat. No. 5,268,171 herein incorporated by reference) that employs PPFMs that have been genetically engineered. The method includes engineering PPFMs to produce a product where the presence of such a product would confer desirable qualities to plants. Once identified and isolated a population of the genetically altered bacteria are placed on or near a plant targeted for improvement. Such bacteria are expected to provide their host plant with the product the bacteria are engineered to produce. The inventors also described a method that uses PPFMs to enhance seed germination (U.S. Pat. No. 5,512,069 herein incorporated by reference). The second method does not specify the genetic makeup or the origin of the PPFMs employed.
One of the inventors also described a method of treating crop plants with a spray treatment of PPFM bacteria to enhance yield (U.S. Pat. No. 5,961,687 herein incorporated by reference). By this method, the application of PPFM bacteria to flowering soybean plants in the field resulted in as great as a 70% increase in yield compared to control plants. This method does not specify the genetic makeup or origin of the PPFMs employed.